The invention relates to a self-energizing disk brake with an electric actuator.
A conventional self-energizing disk brake for passenger cars is disclosed by German Patent document DE 101 643 17.
Self-energizing brakes are known in a very wide variety of embodiments. The drum brakes represent a classic design of self-energizing brakes, where at least one brake shoe is arranged to be leading, with the result that the frictional forces between the brake lining and the drum assist the brake application force.
If, in relatively heavy commercial vehicles, disk brakes having actuating devices which are operated by electric motor are also to be used, the self-energizing disk brake becomes an option. Because it provides the possibility of giving the electric motor smaller dimensions on account of the self-energizing action of the brake than would be possible in the case of a disk brake which is not self-energizing, these brakes make electric actuator possible.
The majority of the known solutions relate to operating principles which, although they make self-energizing possible, are not suitable in general for realizing a disk brake for heavy commercial vehicles which can be produced economically and is ready for series production, on account of the lack of suitability in practice and on account of the complicated structural construction, and they have therefore often not passed the stage of theoretical considerations.
Against this background, the present invention provides a self-energizing disk brake which is operated by an electric motor, has a simple structural construction and realizes a largely uniform wear behavior of the brake disk or the brake disk ring.
In an exemplary embodiment, the brake application unit is designed to move the brake lining or the brake lining unit on a nonstraight path, in particular an arched curve path, parallel to the friction face of the brake disk. The brake application unit includes a crank which has a crank pin which extends parallel to the brake disk axis, and serves to move the brake lining unit tangentially with respect to the brake disk, that is to say parallel to the friction face of the brake disk, and engages positively into a corresponding opening in the pressure plate, with the result that the brake lining unit follows the movement of the crank directly and immediately.
The exemplary design leads to a particularly uniform brake application and to a relatively uniform wear behavior of the brake disk or the brake disk ring, since it is prevented that the linings of the partially lined disk brake dig into the disk in a certain region. In addition, the crank drive is a structurally simple and nevertheless a particularly reliable solution for applying the brake.
In one example, the brake application unit is designed to move the brake lining parallel to the brake disk on a curved path which is approximated to the ring geometry of the brake disk. Here, the expression “curved path” is not to be interpreted too narrowly. In another embodiment, an approximate curved path may be composed of straight chord segments which are oriented at an angle with respect to one another.
If each of the pressure faces of the at least two or more brake plungers which can preferably have their length varied axially by retracting into themselves, is provided at its side which faces the brake lining unit with a recess having a ramp-shaped contour, into which in each case a rolling body engages which is supported on one side on the ramp-shaped contour of the pressure faces of the brake plungers and on the other side on the brake lining unit, the self-energizing brake can be used in a particularly versatile manner and can be controlled reliably. It is preferred in this example if the at least one electric motor drive is designed for actuating the brake application unit or, furthermore, the further electric motor drive is designed for driving the brake plungers at least for changing the axial length of the brake plungers.
In a particularly advantageous example, the ramp-shaped contour is configured in the manner of a groove with a constant or changing ramp angle, which groove describes a curved path.
In order to enable braking operations during forward and reverse driving, it is advantageous, furthermore, if, starting from the lowest point, the ramp-shaped contour describes a curved path in two directions, or forms a curved groove.
The electric motor in this example turns a crank directly or via at least one or more gear mechanisms, which crank has a crank pin which extends parallel to the brake disk axis and engages positively into a correspondingly oriented opening in the pressure plate. This results in a type of rotary bearing is formed, about which the brake linings rotate when they are guided on the curved paths in the ramp faces (the rotary bearing itself moving on a circular path with a small radius).
The curved path preferably has the shape of a circular arc section, the radius of which corresponds to the radius of the circular path, on which the crank moves.
In order to convert the drive movement of the crank into the movement of the brake lining unit, in this example the crank pin engages into a correspondingly oriented opening in the pressure plate.
The compact and inexpensive construction of the self-energizing disk brake is optimized by the fact that the electric motor has an output shaft which is oriented parallel to the brake disk axis and which drives directly or via further gear mechanism elements which are connected in between and likewise have rotational axes which are oriented parallel to the rotational axis of the brake disk, so that a compact construction results which is favorable in terms of production.
In some embodiments, a design of the brake application unit is provided in such a way that it converts uniform rotation of an output shaft of the electric motor drive during a brake application movement into a movement of the brake lining, the movement having a component which is not linear at least in the tangential direction (direction U).
In this way, not only are the production costs of the brake system for commercial vehicles reduced, but the power requirement of the electric motor drive is also minimized considerably by efficient self-energizing with respect to comparable brakes which are actuated electromagnetically and directly, even in the limiting range of the coefficient of friction of the brake lining. According to a particularly advantageous embodiment, it is even possible to reduce the power requirement considerably in comparison with other self-energizing concepts.
In a simple exemplary case, the paths for the rolling bodies or channels have a radius which corresponds to the radius of the curved path of the crank during its movement on a circular path. In this example, the brake lining unit remains oriented parallel to itself during a circumferential displacement, that is to say each point on the brake lining unit performs in each case the same movement. In another example, a rotational movement which has a radius which deviates from the circular path of the crank and is adapted in as optimum a manner as possible to the ring geometry of the brake disk can be superimposed on this movement of the brake lining unit.
As an alternative, according to another exemplary embodiment, cylindrical rolling bodies or rolling bodies which are shaped in another way (for example, barrels) may be utilized, for example, which would then roll on a correspondingly curved groove-like recess in the brake plungers.
The electric motor drive is preferably coupled as an actuator to a control and/or regulating device which is designed for controlling or regulating the position of the actuator and therefore of the brake lining.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.